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More Sirius

StarDate:

December 30, 2012

The Sun and similar stars are steadily losing weight — they blow some of their gas into space through strong “winds.” And at the end, they blow away their entire outer envelopes of gas, leaving behind only their hot, dense cores, known as white dwarfs — tiny remnants of their once glorious selves.

An example is Sirius B, the faint companion to Sirius A, the brightest star in the night sky. Sirius climbs into view in the east-southeast by around 8:30 or 9, and arcs across the south during the night.

Sirius B is too small and faint to see without a telescope. But millions of years ago, that wouldn’t have been the case. The star probably was a few times as massive as the Sun, so it would have shined many times brighter — brighter than Sirius A is today.

Such a hot, bright star produces a much thicker wind than the Sun does, so it loses mass at a higher rate. And because the star was heavier than the Sun, it burned through the nuclear fuel in its core much faster — it burned out in a couple of hundred million years, while the Sun is still only half way through a 10 billion-year lifetime.

As it neared the end of its life, Sirius B puffed up like a giant balloon, then ejected its outer layers. Some of that gas probably piled on the surface of Sirius A, increasing its mass.

Today, Sirius B is as heavy as the Sun, but only as big as Earth. It still shines because it’s extremely hot. But it’s only a dim remnant of its former glory.

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